It is important for rubbery polymers that are used in tires, hoses, power transmission belts and other industrial products to have good compatibility with fillers, such as carbon black and silica. It has also been recognized that the filler in rubber compounds should be well dispersed throughout the rubber, in order to improve various physical properties. Such polymers can be functionalized with various compounds, such as amines and silanes, to attain a improved interaction with filler and a better dispersion of the filler throughout the rubbery polymers. For instance, fillers (such as carbon black and silica) are used in standard rubber compounds for tire treads.
EP 2 196 326 A1 discloses a process for the copolymerization of amine monomer and conjugated diolefin monomer, and that polymers can be terminated with a terminating agent having a hydrolyzable group. One example for the amine monomer is vinylbenzylpyrrolidine. Embodiments of initiation systems include anionic initiators, such as alkyl lithium compounds.
EP 2 772 515 A1 teaches a rubber composition comprising a conjugated diene polymer and a silica. The polymer is obtained by polymerizing a monomer component including (i) conjugated diene compound and (ii) silicon-containing vinyl compound, in the presence of a polymerization initiator. The teaching of this document allows one to obtain elastomers with functional groups that are able to interact with the filler, but these features are achieved by use of additional organosilicon comonomer which is located in the polymer main chain and may deteriorate the processability of rubber. Also, there is no possibility to control weak interactions between rubber and filler, since the amine initiators contain only one amino group.
US 2010/116404 A1 teaches the synthesis of functionalized elastomer derived from styrene, 1,3-butadiene, and an amine-substituted styrene. The functionalized elastomer is used, in admixture with diene-based elastomer, and in further admixture with polyketone short fiber.
U.S. Pat. No. 6,627,722 B2 discloses a polymer containing units of a vinyl aromatic monomer (ring-substituted with one or two alkyleniminealkyl groups) that can be polymerized into rubbery polymers having low hysteresis and good compatibility with fillers, such as carbon black and silica.
EP 2 182 028 A1 teaches modified butadiene rubber having a vinyl content of 35% by weight or less and having, in a main chain, a nitrogen-containing styrene derivative which provides improving rolling resistance performance. The preparation of N-functionalized polymers with different contents of N-functional groups, by incorporation of suitable styrene monomers into the polymer chain, leads to a wide variety of styrene-butadiene rubbers with different content of N-functional groups and thus exhibiting different dispersing properties of inorganic fillers. The N-functionalized styrene derivatives are based on divinylbenzenes.
US 2011/0275756 A1 teaches the synthesis of functionalized SSBR containing amine-substituted styrene and nitrogen-containing silicon-organic groups on the polymer chain end.
U.S. Pat. No. 5,550,203 B teaches anionic initiators for use in polymerizing olefin-containing monomers. The initiators are derived from amines.
Therefore, it was the object of the invention to provide an elastomeric copolymer with controlled micro- and macrostructure and with precisely controlled location of functional groups of a given type which allow controlling the weak interaction between the filler and the rubber, thus influencing tire wet traction and strong interactions which are responsible for rolling resistance. Moreover, these advantages should be achieved without any additional organosilicon or amine comonomer in the polymer main chain, the presence of which might otherwise deteriorate the processability of rubber.
It has now surprisingly been found that this object is achieved and the problems of the prior art overcome by the use of an alkali metal salt derivative of a vinyl aromatic monomer having general formula (A)
wherein                the alkali metal is selected from lithium, sodium, and potassium; and        R is selected from groups of formula (B) and (C):        
wherein                x is an integer of from 1 to 10;        n is an integer of from 2 to 10;        R1 and R2 groups within a repeat unit and in different repeat units are independently selected from a hydrogen atom and an alkyl group having from 1 to 4 carbon atoms; and        R3 and R4 are independently selected from alkyl groups containing from 1 to 10 carbon atoms, aryl groups having 6 to 10 carbon atoms, allyl groups having 3 to 10 carbon atoms, and alkyloxy groups having the structural formula —(CH2)y—O—(CH2)2—CH3, wherein y is an integer of from 1 to 10 and z is an integer of from 1 to 10;as an initiator for the copolymerization of i) one or more conjugated diene monomers and ii) one or more vinyl aromatic monomers.        
The present invention provides copolymer elastomers of dienes with strictly designed micro- and macrostructure and with precisely selected location, type and amount of functional groups in the polymer chain. The copolymers prepared according to the present invention contain two types of functional groups, which performs a balance between strong and weak interactions between polymer and filler (in particular silica and/or carbon black).
A first type of functional group which is chemically bound and incorporated into the polymer chain is a tertiary amine group which provides weak interactions between polymer and fillers (such as silica and/or carbon black). Weak interactions, such as for example hydrogen bonds formed between silica particles and tertiary amino-group from polymer chain, contribute to higher tan δ at 0° C., which corresponds to enhanced wet traction when these types of polymers are used in tread parts of tires.
A second type of functional group may be an alkoxysilyl group (SiOR) and may be chemically bound and incorporated at a terminus of the polymer chain; this allows for the formation of strong intermolecular bonds between polymer and silica. Strong interactions significantly improve (tan δ at 60° C.) which relates to rolling resistance and hysteresis loss, i.e. the failure of a property that has been changed by an external agent to return to its original value when the cause of the change is removed.
Additionally, the introduction of controlled amounts of functional groups of various types, i.e. providing weak and strong interactions with filler, allows the optimal formation of bonds between polymer and filler and thus contributes to enhanced reinforcement and increased abrasion resistance.
The vulcanizable copolymer components of the invention are based on functionalized polymers, and articles prepared therefrom exhibit multiple advantages as compared to the articles based on non-functionalized polymers, particularly with regard to reduced hysteresis at similar or improved wet traction. Furthermore, the modification of the polymer with a combination of functional groups of both types provides far better reduction of hysteresis of vulcanizates in comparison with vulcanizates prepared from non-functionalized compounds or those containing only one type of functional group.
The present invention allows for the preparation of functionalized polymers with controlled micro- and macrostructure and with precisely controlled location of functional groups of a given type. Furthermore, the present invention gives copolymer components comprising fractions Q and T, both being functionalized via various patterns. The content of fraction Q, indicated as x, may range from 0.01- to 100 weight percent, and the content of fraction T, indicated as y, expressed as 100-x weight percent, may range from 99.99- to 0.01 weight percent. The overall content of both fractions typically sums up to about 100 weight percent.

In the above formula, F1 represents the monomer of formula (A), containing a functional group capable of forming weak interactions with filler. F1 can be located at the alpha and/or the omega end of the copolymer;
F2 represents the same monomer as F1, or a different one, and also contains functional group capable of weak interactions, similar or different than in F1. F2 is located more in the centre of the copolymer.
F3 represents the terminal modifying agent as used for the functionalization of the omega terminus of the polymer and typically contains alkoxysilyl groups responsible for strong interactions.
n indicates the number of repeating units of F1, and preferably ranges from 1 to 20 repeating units;
m indicates the number of repeating units of F2, and preferably ranges from 1 to 20 repeating units; p represents the number of polymer chains covalently bound to F3 (derived from the terminal modifying agent), preferably being in a range of from 0 and 10.
J represents the organic residue of the organometallic compound used to prepare the initiator of the invention and may e.g. be an alkyl group, aryl group, phenyl group, protected amine or protected hydroxyl group.
X represents the moiety derived from the coupling agent reacted with the nucleophilic end of the copolymer, the coupling agent typically having general formula X1nYpX2m (E).